Linear methylpolysiloxanes



Patented May 10, 1949 UNITED STATES PATENT OFFICE LINEAR METHYLPOLYSILOXANES Winton I. Patnode, Schenectady, N. Y., assignor to General Electric Company, a corporation oi New York No Drawing. Original application October 29,

1942, Serial No. 463.814. Divided and this application March 8, 1946, Serial No. 653,131

4 Claims.

in which the various R's represent the same or different lower monovalent hydrocarbon radicals selected from the class consisting of lower alkyl. aryl, alkaryl and aralkyl radicals, examples of which are the methyl, ethyl, propyl, phenyl, benzyl, tolyl, xylyl, etc., radicals, and a is a whole number and is equal to at least 3. Preferably the majority of the Rs represent methyl groups when the resulting compounds are used as lubricants.

The term "polysiloxane as used herein refers to the fact that the compounds so designated have a skeletal structure of alternate atoms of silicon and oxygen. The structure may be either of the straight or of the branched-chain type. A formula for the linear or straight-chain compounds is where the various Rs have the same significance as given above, and n is an integer (positive integer) equal to at least 1. A formula for the simpler branched-chain compounds is In "I R O-i- R R-Eii-R where R and n have the same meanings as given above.

As an example of the more complex type of branched-chain polysiloxane, the following is given:

IV a

n-si-R RSi-R The compounds embraced by Formula I are distinguished from all other known organo-silicon compounds by the following criteria:

1. Each silicon atom is joined to at least one other silicon atom through an oxygen atom.

2. Oxygen atoms are found only between silicon atoms.

3. The ratio of the number of R groups to the number of silicon atoms is fixed and is equal to where a is the number of silicon atoms.

4. Each terminal silicon atom of the skeletal structure is joined directly to three R groups. Thus it is seen that although the number of individual compounds coming within the scope of Formula I is large, the class of compounds is narrowly defined by these four criteria. Examples of specific chemical compounds included in this classification are:

such

9. Dimethyl tetra-(trimethylsiloxy) disiioxane' AKCH 10. Symmetrical 1,3-hexaphenyi-2-dimethyltrisiloxane (CHdii (CH3) aSi-O-SflCoI-Is) a-Si(CH:l) 3

l2. 1,3 hexamethyl-2-methyl-2-phenyltrisiloxane (CH1) 1SiOSi(CHs) (CtHs) -O-Si(CH3) a In the system of nomenclature adopted in naming the above compounds, the individual silicon atoms in the Si-O-Si chain have been designated by numerals, the SiO group in which the oxygen is connected to a second silicon atom has been called a siloxy" group, and the compound containing them a siloxane." On this basis the com und I-IaSi-O-SiH: is known as disiloxane with the prefix indicating the number of silicon atoms in the chain. The system resembles somewhat the Geneva system of nomenclature of organic compounds.

The novel compounds herein described are useful for diverse purposes. For example, they may be used as intermediates in the preparation of other complex silicon compounds. They also may be employed as plasticizers or softeners for various resins, including the silicone resins such as those described and claimed in Rochow U. 5. Patents 2,258,218-222. Liquid mixtures of the various compounds represented by above formulas also may be used as electrical insulating fluids, damping fluids, etc. Such mixtures are particularly useful as lubricants as will be described more fully hereinafter. More complex or resinous silicon compounds may be prepared by treating my compounds in such a manner as to oxidize one or more of the hydrocarbon radicals to form compounds capable of further condensation with one another. The more viscous materials may be employed as waterproof impregnating agents by application from solution.

The preferred process used in the preparation of these novel polysiloxane derivatives, briefly described, comprises treating a mixture of an organodisiloxane having the general formula RsSiOSiR.3 and a silicone or polysiloxane having the general formula wherein m is not greater than 2, with a small amount of concentrated sulfuric acid at room temperature, separating the acid layer, and washing the remaining polysiloxane layer with water.

A second process comprises the hydrolysis of mixtures of organohalogenosilanes, one member of which is represented by the formula RaSlX and the other members of which are chosen from the class consisting of RhSiXs, RSiXs and sun. where R has the meaning hereinbefore given and X represents a halogen atom. The product of hydrolysis is likewise separated from the acid. In this method of preparation, the average composition of the mixture of hydrolyzable silanes should correspond to the formula RbSiXu-b), where b is substantially greater than 2, preferably greater than about 2.5, and is less than 3. For maximum yields of the chain compounds, it may be desirable to follow this hydrolysis process by treatment of all or part of the products with sulfuric acid as described briefly above.

A third general process, especially suitable for introducing phenyl groups into the molecule, comprises treating a mixture of an organodislloxane of the formula Ram-041R: and an organosilanediol such as diphenylsilanediol,

(CeHslzSflOHla, with a small amount of con centrated sulfuric acid. Other polysiloxanes, of which octamethylcyclotetraslloxane,

[(CHshSlOls boiling at C. is an example, may be added to the starting materials. These cyclopolysiloxanes are more fully described in my copending application Serial No. 463,813, flied October 29, 1942, now abandoned and assigned to the same assignee as the present invention.

A fourth general process comprises bringing together, with or without a solvent, a silanol of the type RsSlOH and an organohalogenosilane of the type RzSlXz. An alternative procedure is to permit a silanediol of the type RoSflOH): to react with a monohalide of the type RsSiX. Other more complex silanols in which the presence of Si0H groups is noted, but which are so complex as to defy a determination of exact structure, may likewise be permitted to react with halides of the type RaSlX, or may be caused to react with disiloxanes of the type R:SiO-SiRs.

It is to be noted that all four of these general procedures require as part of the starting material an organo-silicon compound containing the group R3Si, which emerges from the reaction as a terminal grouping of the skeletal chain or branched-chain structure of the molecule. Depending on the starting materials used, the products obtained may or may not comprise complex mixtures of the various chain compounds which cannot be separated from each other and individually identified by ordinary analytical means. Consequently, in most of the following specific examples, given for purpose of illustration, I have chosen comparatively simple, chemically pure starting materials which permit a separation of the individual products of reaction one from another. Examples of such simple starting materials are hexamethyldisiloxane,

octaphenylcyclotetrasiloxane, (CsHs) zSiOh; diphenylsilanediol, (CaHsMSHOI-Da; hexamethyicyclotrisiloxane, [(CH3):SiO]:; trimethylchlorosilane, (CI-IahSiCl; methyltrichlorosilane, CHsSiClz; silicon tetrachloride, SiCll; etc.

EXAMPLE 1 An equimolar mixture of hexamethyldisiloxane, (CHa) aSlOSi(CH3) s, and of octamethylcyclotetrasiloxane, [(CI-IalzSiOh, was shaken with 10 per cent of its weight of concentrated sulfuric acid at room temperature for four hours. The lower layer of acid was separated and the upper layer of polysiloxanes was washed free of acid with water, dried over anhydrous potassium carbonate, and fractionally distilled. The following compounds were separated and identified:

1. Octamethyltrisiloxane 2. Decamethyltetrasiloxane 3. Dodecamethylpentasiloxane 4. Tetradecamethylhexasiloxane These compounds are methylpolysiloxanes corresponding to the formula I- OH;

where n represents an integer (positive integer) which is at least 1 and not more than 4. The properties of these compounds are set forth in asoaaeo following table in which the compounds are designated by the above reference numerals.

Ilium.

Representative analyses of these compounds are given below:

Found Theoretical Compound In addition to the compounds listed, there remained after fractional distillation a high-boiling residue believed to comprise compounds of the same series, CHaHCHzhSiOhSHCHsls. where n is larger than 5. It is to be noted that none of the starting compound octamethylcyclotetrasiloxane was found in the products of the reaction. Although in the above example an equimolar mixture of the two reactants was used, the invention is not limited thereto. An increase in the proportion of the disiloxane derivative used is believed to favor the formation of the lower polysiloxane chain compounds, while a decrease in the proportion of disiloxane derivative results in the formation of larger quantities of the products of higher molecular weight which are not readily separated from each other by distillation.

The following example illustrates an alternative process of preparing compounds of the kind embraced by Formula I and likewise illustrates the preparation of simple branched chain derivatives.

EXAMPLE 2 A mixture of methyltrichlorosilane and trimethylmonochlorosilane in the ratio of 0.67 mol of the former to 2.69 mols oi the latter compound was hydrolyzed by adding it to 700 cc. of violently stirred water cooled externally so that the maximum temperature of the reaction mixture was 32 C. Two liquid layers were formed. The lower aqueous layer was discarded, and the upper layer was washed with water and dried over anhydrous potassium carbonate. This liquid was divided by distillation into three portions: (A) chiefly hexamethyldislloxane, (B) a fraction boiling up to 200 C. at 1 mm. pressure, and (C) a non-volatile oil. FractionsA and C were recombined and shaken with a small quantity of sulfuric acid. The oil was then washed free of acid with water, dried and distilled as before, whereupon more of the (B) fraction was obtained. On fractional distillation oi the B iractions, the compound K DI molecular weight: found, 316, theoretical, 310.5. Analysis for C, H and 81 gave the following results:

Found Theoretical In addition to methyl tri-(trimethylsiloxy) silane, some hexamethyldisiloxane was isolated, and there remained a relatively non-volatile oil which contained more complex compounds, the simplest of which were probably compounds represented by the general formula where n is an interger greater than 1.

The following example illustrates a process for preparing compounds of the kind embraced by Formula I in which the various R's in the general formula are represented by diflerent hydrocarbon radicals, and in which a silanediol of the type RaSflOI-Ila is used as one of the starting materials.

EXAMPLE 3 A mixture of hexamethyldisiloxane and diphenylsilanediol in the proportions of 41 grams of the former to 54 grams of the latter was agitated with 30 grams of concentrated sulfuric acid for 10 minutes at room temperature. The crystalline diphenylsilanediol is substantially insoluble in the hexamethyldisiloxane, but on shaking with the acid the two materials react to form a single liquid phase which is lighter than the acid. An equal volume of water was added to the two-phase system, which was extracted with an equal volume of ether. The ether extract was dried over anhydrous sodium sulfate, and the liquid fractionally distilled. The compound, symmetrlcal 1,3-hexamethyl-2-diphenyltrisiloxane, having the formula dzo, 0.9728 g./cc.; Na, 1.4927; molecular weight: found, 360, theoretical, 360.4.

Analysis:

Found Theoretical The residue remaining in the flask was a viseous liquid at room temperature, and is presumed to contain complex compounds of the general formula Example 4 illustrates a further method of preparation of the novel compounds of this invention, also utilizing diphenylsilanediol.

Exsmrnn 4.

Twenty-five grams of diphenylsilanedfol dissolved in 325 cc. of ether was added drop by drop below the surface of 25 g. of trimethylchlorosllane dissolved in cc. of ether. The reaction mixture was stirred violently throughout the addition, which required a period of one hour. After removal of the ether by distillation, the remaining liquid was fractionally distilled. In addition to hexamethyldisiloxane, a yield of 12% o! symmetrical 1,3-hexamethyl-2-diphenyl trisiloxane was obtained. The residue in the flask was a viscous, high-boiling liquid which is believed to comprise a mixture of compounds of the type cmnsloflclnliisi}..si cii.). where n is an integer greater than 1.

The reactions which take place during the formation of the compounds embraced by Formula I depend, of course, upon the nature of the starting materials. When neither of the reactants is a halide, but consist largely of slloxanes, the role of the concentrated sulfuric acid is to open the si-O-Si linkage iollowed by recombination of the fragments thus formed in new positions, probably by the momentary formation of esters of sulfuric acid followed by hydrolysis of these esters to form new compounds. This is borne out by the fact that the chemical structure oi. the new compounds indicates that the R groups attached to a given silicon atom are not separated therefrom at any time during the reaction, but that the breaking and recombination of the parts of the starting materials always take place at an Si-O-Si linkage. I When the starting materials are both organohalogenosilanes in the proper proportions, and the reaction is carried out in water, the reaction is believed to be hydrolysis oi the halogen and condensation of any silicols formed, resulting in the final polysiloxanes. Any cyclic compounds formed during the reaction and containing the Si-O-Si linkage are opened by treatment with sulfuric acid and recondensed with fragments of other compounds having terminal RsSi-- groups to form the desired chain compounds. When one of the starting materials is a halide and the other is a silanol or silanediol, then the reaction is believed to be a splitting out of 1101 with the direct formation 01. a siloxane bond.

Whenever one of the starting materials consists 01' a compound in which two diflerent hydrocarbon radicals are attached to the same silicon atom, the silicon atoms of the resultant compounds will be similarly substituted. A representative reaction of this type would be that between symmetrical diphenyltetramethyldisilexam and a cyclic polymer of methylphenylsilanone to form compounds of the formula wherein n is a whole number equal to at least 1.

All oi. the chain compounds prepared as herein described are liquid in form. They are to be distinguished from other liquid organo-silicon compounds comprising carbon, hydrogen, silicon and oxygen by their unique properties. For example, whereas esters of silicic acid, such as ethyl silicate, or esters of organo-substituted sllicic acids likewise are liquids comprising carbon, hydrogen, silicon and oxygen, they are susceptible to hydrolysis by water, often yielding gels or resins. The compounds embraced by Formula I are stable toward water. Furthermore, whereas some of the hydrolysis prodffcts or organohalogenosilanes described in Rochow U. S. Patents 2,258,218-222 are liquid in nature, they rapidly become resinous on heating, due, as is pointed out in those patents, to the fact that they comprise compounds in which the ratio of organic radicals to silicon atoms is less than 2. The viscous liquids embraced by Formula I, in which the aforementioned ratio is greater than 2, are not readily converted to resins on heating, but on the contrary maintain their liquid form for long periods of heating, thus enhancing their suitability as lubricants or heat-transfer media. The simple organodisiloxanes oi the type RaSi-O-SiRa, among which is hexamethyldisiloxane, are relatively i'luld compounds of low viscosity and low boiling point, or ii the B group is very large, contain a. disproportionate amount oi carbon and hydrogen at the expense of the silicon and oxygen; whereas the compounds embraced by Formula I, having a ratio of R groups to silicon atoms less than 3, possess the desirable properties of the siloxane bond in much greater degree.

Certain substituted cyclopolyslloxanes oi the general formula [RiSiOln having an oxygen to silicon ratio of 1, which are i'urther described in my copending application Serial No, 463,813 mentioned above, are also liquids but they differ from the compounds covered by Formula I in certain important characteristics. For example, octamethylcyclotetrasiloxane and decamethyitetrasiloxane are similar in chemical composition in, respectively, having the formulas (CH4) |8i40 and (CHIUIOSMOL and boiling at 175 C. and 194' C., respectively. Their freezing points, however, difler widely, being C. and 68 C., indicating the superiority oi the chain compounds embraced by Formula 1 in uses where a polysiloxane is subjected to low temperatures, such for example as in a lubricant or damping fluid. A simiiar unique property of the compounds or the present invention, for example tetradecamethylhexasiloxane, resides in their relatively small change in viscosity with temperature when compared with the much larger change in viscosity with temperature exhibited by the similar cyclic compounds. This diflerence in properties is likewise found in complex mixtures of the same two types of materials. Various differences between certain straight chain polysiloxanes of the type described herein and the corresponding cyclic or ring type polydimethylsiloxanes are brought out in the following table:

Properties of cyclic polymers [(CHnzSiOh Viscosity, Number 0! am Vis.,

Moms B. Pt., 0. F.Pt.,0. 2,

4 115 11.5 2.20 0.96 2.129 a 210 --31 as: 1.56 2.45 a 245 -2 as; 2.54 an Properties of polymers CH:[ (CHzhSiOlnSflCHil:

Viscosity, Number of I tatio Vis.

Moms B. PL, 0. F. Pt., 0.

Thus it is seen that the linear or straight chain compounds boil higher, freeze lower, have lower viscoslties, and have smaller changes in viscosity with temperature than do the corresponding ring compounds containing the same number of silicon atoms. The more favorable viscosity index of the chain compounds is even more pronounced when examined on a logarithm viscosity-reciprocal temperature chart. These diflerences indicate EXAMPLE 5 The following mixtures of hexamethyldisiloxone (A), octamethylcyclotetrasiloxane (13), diethyl ether and concentrated sulfuric acid were shaken together at room temperature for periods of time exceeding four hours. The acid was then washed out with water, the ether was removed by distillation, and the remaining oil was heated up to 300 C. to distill out the low boilers, leaving residues of oils of varying visoosities.

Preparation cc. cc. cc. cc. cc. Distillate Number A B other H1804 below 300 C.

The most viscous of all the oils was preparation I, which contained no (CH3)3Si groups. Oils of this type are more fully described and claimed in my copending application Serial No. 463,815 filed October 29, 1942, now abandoned and assigned to the same assignee as the present invention. As is described in that application, such products consist primarily of cyclic, polymeric dirnethyl sllanones of the formula [(CI-Ix) 2810]: wherein a: is an integer greater than 10. This material would just barely flow at room temperature. The most fluid of all was II, which contained the greatest amount of (CHshSi groups, and had a viscosity of about 4 cp. The others increased in viscosity as the proportion of (A) was decreased, up to VI, which had about the viscosity of a medium grade motor oil. When kept at the temperature of solid carbon dioxide (80 C.) for a day. sample II was very fluid, samples III and IV were less fluid but would pour, while the remainder oi the oils were more or less crystalline or solid.

This example illustrates the effect of changing the proportion of hexamethyldisiloxane in the starting material. It is to be noted that although both of the starting materials boil below 200 C. they react to form oils substantially non-volatile at 300 C., which oils will pour at -80 C. It will also be noted that as the proportion of (A) increased, the final products contained greater proportions of chain compounds and smaller proportions of the above-mentioned cyclic compounds, resulting in a decrease of the pour points and viscosities of the oily products.

The following example illustrates a method of preparation of an oil of about the viscosity of a light motor oil.

Exams: 6

Ninety-three grams of hexamethyldisiloxane, 593 g. of octamethylcyclotetrasiloxane and 120 cc. of concentrated sulfuric acid were shaken together at room temperature for 20 hours. The lower acid layer was drawn oiT from a separatory funnel and the upper oily layer was washed free of acid with water, filtered, and dried over anhy. drous potassium carbonate. A sample of the light oil thus obtained was placed in a beaker along with a piece of iron and a piece of copper at a temperature of C. After being continuously exposed to the air at this elevated temperature for a period of 6 weeks, the oil remained waterwhite in color, did not deposit sludge nor develop acidity, and the pieces of metal were not corroded. Under the same circumstances a petroleum oil would have deteriorated badly.

During this period of time, from V4 to $6 of the oil evaporated. In order to avoid this evaporation. the bulk of the oil was placed in a flask. and V5 of it was distilled out under vacuum. The residue was somewhat more viscous than the distillate, having the following viscosities at the indicated temperatures.

At 212" F. the oil had a viscosity of 6.7 cp., which increased to 24 cp. on cooling to 68 F.. a 3 to 4-fold increase. A petroleum oil of similar viscosity increased in viscosity from about 4 centistokes at 212 F. to about 30 centistokes at 68 I"., an increase of 7 to 8-fold. This comparison again shows the superiority of the polysiloxane oils over petroleum oils.

Methylpolysiloxane oils hereindescribed are particularly suitable for lubrication under oxidizing conditions at elevated temperatures, at very low temperatures, and in locations where wide temperature fluctuations are experienced. They should be particularly suitable for the lubrication of instrument bearings by virtue of their freedom from gum formation. They should likewise be particularly useful in locations where it is inconvenient to continually add lubricant to a hearing or where it is inconvenient to clean it.

Their maintenance of water-white color even under extreme oxidizing and sunlight conditions makes these compounds especially suitable for use as softeners or plasticizers for colorless or light-colored resins or films.

Their stability toward oxidation and discoloration in the presence of copper, as well as their freedom from acid-forming tendencies. makes them particularly suitable for insulating fluids.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A methylpolysiloxane corresponding to the formula OH where n represents an integer which is at least 1 and not more than 4.

2. Decamethyltetrasiloxane. 3. Dodecamethylpentasiloxane. 4. Tetradecamethylhexasiloxane.

WINTON I. PATNODE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Certificate of Comctlon Patent No. 2,469,890. May 10, 1949.

WINTON I. PATN ODE It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, for that portion of the formula. following line 15, reading:

-sa-o -s1-o uann. read imam).

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 22nd day of November, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uommiaaimer of Patents. 

